Patent Application
20070089417
The present invention relates generally to catalytic reformers, and more specifically to catalytic reformers for gas turbine engines that include a downstream support.
Engineers are constantly seeking strategies of reducing undesirable combustion emissions, such as nitrogen oxides (NOx). For instance, stringent government regulations limiting the amount of NOx that can be emitted from gas turbine engines has driven the industry to produce gas turbine engines with NOx emissions levels below 3 ppm. Over the years, engineers have found that the lower the ignition temperature of combustion, the less NOx the combustion will produce. Thus, in order to achieve lower emissions levels, pre-combustion catalytic reformers that reduce the ignition temperatures required for complete combustion of a fuel-air mixture are being used within gas turbine engines.
In a gas turbine engine, the catalytic reformer is generally positioned within a combustor assembly and downstream from a compressor assembly. The compressor assembly compresses ambient air, and delivers a portion of the compressed air to the combustor assembly to be mixed with fuel. Within the catalytic reformer, the fuel-air mixture passes over tubes within a tube bundle that are coated with a catalyst. The fuel-air mixture reacts with the catalyst creating radicals which aid in stabilizing the flame downstream within the combustor assembly.
However, because many catalysts will not react with the fuel-air mixture at the temperature of the compressed air leaving the compressor assembly, a fuel rich mixture is often needed to react with the catalyst. Thus, not all of the compressed air leaving the compressor assembly will be mixed with the fuel. A portion of the compressed air that is not mixed with the fuel can flow through each tube within the tube bundle of the catalytic reformer in order to absorb the heat from the tube bundles caused by the catalytic reaction.
Once the fuel-air mixture passes along the outer surfaces of the tubes and the compressed air passes within the tubes, the catalyzed fuel-air mixture and the compressed air are mixed together in a mixing chamber before being delivered to a combustor chamber. By mixing the fuel with all the compressed air prior to combustion, the risk of hot spots within the combustion chamber is reduced and a relatively uniform temperature can be maintained during combustion, leading to reduced NOx production.
Although the catalytic reformers have succeeded in reducing NOx emissions, the catalytic reformers are subjected to hostile environments within the gas turbine engines. For instance, high temperatures can be created by the reaction between the catalyst and the fuel, pre-ignition within the catalytic reformer, and/or flashback ignition from the downstream combustion. Vibrations can be caused by the flow of the cooling air inside the tubes, flow of the fuel-air mixture passing over the tubes, and other system vibrations within the engine. Moreover, oxidation can cause corrosion within the catalytic reformer. Eventually, the stress of the high temperatures, the vibrations and/or corrosion may cause one of the tubes within the tube bundle to fail and break away. The tube may be forced downstream into a turbine assembly and severely damage the engine.
In order to support and secure the tubes within the catalytic reformer, the catalytic combustor cooling tube vibration dampening device described in U.S. Patent Application No. US 2003/0056511 A1, by Bruck et al. on Mar. 27, 2003, includes regions on each tube within the bundle that maintains tube to tube contact to supposedly better resist vibrations. Thus, rather than the tubes impacting one another during various modes of vibration, the tubes rigidly support one another at the contacting regions.
Although the tube to tube contact within the tube bundle of the Bruck catalytic combustor may dampen the vibrations on the tube bundle, the tube to tube contact reduces the outer surface area of the tubes that can be coated with the catalyst. Thus, there is less surface area for the catalyst to react with the fuel-air mixture, thereby reducing the fuel-air mixture's ability to stabilize of the downstream flame during combustion. Further, the costs of manufacturing and installing the tubes with the contacting portions may be relatively high.
The present invention is directed at overcoming one or more of the problems set forth above.
In one aspect of the present invention, an apparatus includes an apparatus housing that defines at least one first flow inlet and includes an upstream support and a downstream support. The upstream support defines a plurality of second flow inlets, and the downstream support defines a plurality of outlets that includes a first portion and a second portion. At least one first flow path is defined by a plurality of surfaces, and fluidly connects the first flow inlet to the first portion of the plurality of outlets. At least one of the plurality of surfaces is coated with a pre-combustion catalyst. A plurality of second flow paths is defined by a plurality of tubes that extend between the plurality of second flow inlets and the second portion of the plurality of outlets.
In another aspect of the present invention, an apparatus includes means for securing a plurality of tubes that extend between an upstream support and a downstream support within an apparatus housing. The apparatus also includes means for introducing a fuel-air mixture flow outside the plurality of tubes and a means for introducing an air flow within the plurality of tubes. The fuel-air mixture flow is introduced via at least one first flow inlet defined by the apparatus housing, and the air flow is introduced via a plurality of second flow inlets defined by the upstream support. There are means for contacting the fuel-air mixture flow with a pre-combustion catalyst, and means for delivering the air flow and the fuel-air mixture flow to a mixing chamber via a plurality of outlets defined by the downstream support.
In yet another aspect of the present invention, a method of assembling an apparatus includes a step of forming at least one first flow path and a plurality of second flow paths through an apparatus housing. A first end of a plurality of tubes is attached to a plurality of second flow inlets defined by an upstream support, and a second end of the plurality of tubes is attached to a portion of a plurality of outlets defined by a downstream support. At least one surface of the first flow path is coated with a pre-combustion catalyst.
Referring to
The catalytic reformer 16 is in fluid communication with the compressed air plenum 18 via a plurality of compressed air inlets 21 and pre-combustion mixing regions 25. The catalytic reformer 16 is also in fluid communication with a fuel supply system that includes fuel injectors 22 that inject fuel into the pre-combustion mixing regions 25. Within the catalytic reformer 16, a first portion of the compressed air enters the pre-combustion mixing regions 25 and mixes with fuel injected by the fuel injectors 22 to create a rich fuel-air mixture. The rich fuel-air mixture reacts with a pre-combustion catalyst 41 (shown in
The combustor assembly housing 15 defines a mixing chamber 32 downstream from the catalytic reformer 16 and upstream from the combustor 13. The catalytic reformer 16 is in fluid communication with the mixing chamber 32 via a plurality of outlets 31. After passing through the catalytic reformer 16, the rich fuel-air mixture and the compressed air will mix within the mixing chamber 32 to form a lean fuel-air mixture. The lean fuel-air mixture is delivered to a combustor 13 in which it is ignited to create a working gas. The working gas is delivered to the turbine assembly in which it is expanded through a series of rotatable blades that are attached to the shaft and stationary vanes. The blades and shaft rotate creating a mechanical force.
Referring to
The catalytic reformer 16 includes means 48 for securing the plurality of tubes 36 extending between the upstream support 34 and the downstream support 30. Although the tubes 36 are illustrated as cylindrical, it should be appreciated that the tubes 36 could be of various shapes. A first end 46 of the plurality of tubes 36 is attached in fluid communication with the compressed air flow inlets 21 defined by the upstream support 34, and a second end 47 of the plurality of tubes 36 is attached in fluid communication with the compressed air outlets 31b defined by the downstream support 30. The plurality of tubes 36 can be secured to the upstream and downstream supports 34 and 30 by various methods. However, the ends 46 and 47 of the tubes 36 and the supports 34 and 30 are preferably brazed to one another in a conventional manner.
The catalytic reformer 16 includes at least one first flow path, being the fuel-air mixture flow paths 39, and a plurality of second flow paths, being the plurality of compressed air flow paths 35. Each of the flow paths 35 and 39 are illustrated by arrows in
The catalytic reformer 16 includes means 43 for introducing the compressed air flow into the compressed air flow paths 35. The means 43 includes the upstream support 34 that is preferably a relatively non-porous metal plate that defines the plurality of compressed air flow inlets 21. In the illustrated catalytic reformer 16, the reformer housing 33 includes a second upstream support 27 that defines a plurality of tube bores 28 that include a diameter greater than a diameter of each tube within the plurality 36. The plurality of tubes 36 are received within the plurality of tube bores 28. Thus, an area between the outer surface 40 of each tube and an inner surface of the tube bore 28 can serve as a portion of the fuel-air mixture flow paths 39. The catalytic reformer 16 includes means 42 for introducing the fuel-air mixture flow into the fuel-air mixture flow paths 39. The means 42 includes the circumferential housing 37 that defines the fuel-air mixture inlets 29 and the pre-combustion regions 25. Although the present invention is illustrated as including two fuel-air mixture inlets 29, it should be appreciated that the circumferential housing 37 could include any number of fuel-air mixture inlets, including one.
The catalytic reformer 16 includes means 44 for contacting the fuel-air mixture flow with the pre-combustion catalyst 41. The means 44 includes at least one of the plurality of surfaces 38 that define the fuel-air mixture flow paths 39 that fluidly connects the fuel-air mixture inlet 29 with the fuel-air mixture outlets 31a. Although any one of the plurality of surfaces 38 can include a coating of the pre-combustion catalyst 41, the outer surfaces 40 of the tubes 36 preferably include the coating of the pre-combustion catalyst 41. Thus, as the fuel-air mixture flows through the fuel-air mixture flow paths 39, the fuel-air mixture can make contact with the pre-combustion catalyst 41. Those skilled in the art will appreciate that there are a variety of pre-combustion catalysts that can be coated on the outer surfaces 40 of the tubes 36, including, but not limited to, platinum and palladium. Those skilled in the art will also appreciate that a reaction between the fuel-air mixture and the pre-combustion catalyst 41 can reform the fuel. The reformed fuel is richer in hydrogen, which can ultimately result in lower NOx emissions during combustion.
The catalytic reformer 16 includes means 45 for delivering the compressed air flow and the fuel-air mixture flow to the mixing chamber 32 via the fuel-air mixture outlets 31a and the compressed air outlets 31b defined by the downstream support 30. The fuel-air mixture outlets 31a preferably include pores defined by a material comprising the downstream support 30, and the compressed air outlets 31b preferably include outlets of the plurality of tubes 36. Thus, the fuel-air mixture flow will preferably pass through the pores to the mixing chamber 32, and the compressed air will preferably pass through the tube outlets to the mixing chamber 32. Within the mixing chamber 32, the rich fuel-air mixture can mix with the compressed air to create the lean fuel-air mixture that is delivered to the combustor 13.
The downstream support 30 preferably includes a plate, and the plate is preferably comprised of a powdered metal with a predetermined porosity. Because the downstream plate 30 is preferably made from powdered metal, the plate 30 is rather simple and economical to manufacture. Those skilled in the art appreciate that there are various sized powdered metals that can be used to form the downstream plate 30 with the predetermined porosity by use of a sintering process known in the art. The size of the powdered metal will be selected based on the predetermined porosity. The predetermined porosity is the porosity required to achieve a desired volumetric flow rate of the fuel-air mixture through the downstream plate 30 to the mixing chamber 30 at a known pressure differential. The larger the desired volumetric flow rate through the downstream plate 30, the greater the porosity of the downstream plate 30. Thus, by controlling the porosity of the downstream plate 30, along with the air-split between the compressed air flow paths 35 and the fuel-air mixture flow paths 39 prior to entering the catalytic reformer 16, the amount of fuel-air mixture mixing with the compressed air, and thus, the amount of fuel, within the lean fuel-air mixture that is delivered to the combustor 13 can be controlled. Those skilled in the art will appreciate that it is important to accurately control the fuel and air percentages of the lean fuel-air mixture that is combusted in order to limit the NOx and other undesirable emissions, from the gas turbine engine 10.
Referring to
In order to assemble the catalytic reformer 16, the compressed air flow paths 35 and the fuel-air mixture flow paths 39 are formed by attaching the first end 46 of the plurality of tubes 36 to the upstream plate 34 and the second end 47 of the tubes 36 to the downstream plate 30. Preferably, the outer surfaces 40 of the tubes 36 are coated with the pre-combustion catalyst 41 prior to the attachment of the tubes 36 to the plates 34 and 30. It should be appreciated that the tubes 36 can be coated with the pre-combustion catalyst 41 in any manner known to those skilled in the art or can be purchased pre-coated. It should further be appreciated that any one of the plurality of surfaces 38, such as an inner surface of the circumferential housing 37, could also be coated with the pre-combustion catalyst rather than, or in addition to, the coating on the outer surface 40 of the tubes 36.
The upstream plate 34 is manufactured to define the plurality of compressed air inlets 21 that can receive the first end 46 of the plurality of tubes 36. The upstream plate 34 is preferably manufactured from a non-porous material, thereby restricting the passing of the compressed air to the plurality of compressed air inlets 21 defined by the plate 34. In the illustrated examples, the tubes 36 also extend through the tube bores 28 of the second upstream support 27. The tubes 36 are inserted into the tube bores 28 such that there exists an area between the outer surface 40 of the tubes 36 and the inner surface of the tube bores 28 through which the fuel-air mixture can flow. The downstream plate 30 is manufactured to define the compressed air outlets 31b that can receive the second end 47 of the tubes 36. The downstream plate 30 is also manufactured to define the fuel-air mixture outlets 31a. Although the fuel-air mixture outlets 31a can be formed by various means, such as drilling passages through the downstream plate 30, the fuel-air mixture outlets 31a are preferably formed by comprising the downstream plate 30 from a porous material, preferably a powdered metal with the predetermined porosity. The predetermined porosity is the porosity required to achieve the desired volumetric flow rate of the fuel-air mixture through the downstream plate 30. The desired volumetric flow rate is a function of the predetermined percentage of fuel within the lean fuel-air mixture that will result in the least amount of NOx and other undesirable emissions. The desired volumetric flow rate, and thus the predetermined porosity, for a known pressure differential across the downstream plate 30 can be determined by any method known in the art. Although the tubes 36 can be secured to the plates 34 and 30 by various methods known in the art, the tubes 36 are preferably secured to the plates 34 and 30 by brazing the first end 46 of the plurality of tubes 36 to the upstream plate 34 and the second end 47 of the tubes 36 to the downstream plate 30.
Preferably, the circumferential housing 37 is attached to the upstream plate 34, the second upstream plate 27 and the downstream plate 30. The present invention contemplates the circumferential housing 37 being attached to the plates 34, 27 and 30 by various methods, including, but not limited to, welding the housing 37 to each plate 34, 27 and 30. Although the circumferential housing 37 defines the fuel-air mixture inlets 29, the present invention contemplates a reformer housing without a circumferential housing. For instance, the engine housing could be shaped to house the tubes and end plates.
Thus, in the assembled catalytic reformer 16, each tube within the plurality 36 defines a compressed air flow path 35 extending between one inlet of the compressed air inlets 21 and one of the compressed air outlets 31b. It should be appreciated that the present invention contemplates any number of tubes defining compressed air flow paths 35. Further, the plurality of surfaces 38 (outer surface of tubes 36 and inner surface of housing 37) define the fuel-air mixture flow paths 39 fluidly connecting the fuel-air mixture inlets 29 with the fuel-air mixture outlets 31a.
Compressed air will flow to the compressed air flow paths 35 from the compressor assembly via the compressed air plenum 18 that surrounds the catalytic reformer 16. The compressed air can pass through the catalytic reformer 16 via the plurality of tubes 36 to cool the tubes 36 from the heat of the reaction between the pre-combustion catalyst 41 and the fuel-air mixture. In addition, compressed air, delivered from the compressor assembly via the compressed air plenum 18, and fuel, injected by the fuel injector 22, will enter the reformer via the fuel-air mixture inlets 29 and mix within the pre-combustion mixing area 25. The fuel-air mixture can separately pass through the catalytic reformer 16 on the outsides of the tubes 36, and contact the pre-combustion catalyst 41 on the outer surfaces 40 of the tubes 36. The fuel-air mixture and the compressed air can both pass through the downstream plate 30 via the fuel-air mixture outlets 31a and the compressed air outlets 31b, respectively, to the mixing chamber 32. The predetermined porosity of the downstream plate 30 will allow the desired volumetric flow rate of the fuel-air mixture to pass through the fuel-air mixture outlets 31a. In the mixing chamber 32, the compressed air and the desired amount of fuel-air mixture will mix to form a relatively uniformly mixed lean fuel-air mixture which is appropriate for combustion with reduced levels of NOx emissions. The lean fuel-air mixture is delivered to the combustor 13, in which it is combusted. The energy created by the combustion drives the turbine which is operably coupled to drive the compressor.
The present invention is advantageous because it provides structural support and containment for the catalytic reformer 16. Because the catalytic reformer 16 is subjected to a relatively hostile environment, including, but not limited to, vibrations, heat and corrosion, the tubes 36 must be adequately supported. The upstream and downstream plates 34 and 30 provide structural support to the tubes 36 in order to decrease the likelihood of tube breakage or failure. However, if a reformer component fails due to the hostile environment, the downstream plate 30 can contain the broken reformer component within the reformer 16. For instance, if one of the tubes 36 were to fail due to vibrations, heat and/or corrosion, the downstream plate 30 would prevent the broken portion from being delivered downstream to the turbine 17 and potentially severely damaging the engine 10.
Moreover, the upstream and downstream plates 34 and 30 provide structural support and containment without interfering with the desired flow paths 35 and 39 of the compressed air and the fuel-air mixture through the catalytic reformer 16. The compressed air is exclusively introduced into the plurality of tubes 36; whereas, the fuel-air mixture is exclusively passed on the outside of the tubes 36. The compressed air can cool the tubes 36 on which the fuel-air mixture is making contact with the pre-combustion catalyst 41. Both the compressed air and the fuel-air mixture can flow through the outlets 31 and mix in the mixing chamber 32. Thus, the upstream and downstream plates 34 and 30 allow the fuel-rich mixture to make contact with the pre-combustion catalyst 41 while the fuel-lean mixture is delivered to the combustor 13. Thus, the catalytic reformer 16 can reduce NOx emissions without using an expensive exhaust clean up system.
In addition, the present invention is advantageous because the fuel to air ratio in the lean mixture delivered to the combustor 13 can be accurately controlled by controlling the porosity of the downstream plate 30. Engineers can select the porosity that allows the desired volumetric flow rate of the fuel-air mixture to pass to the mixing chamber 32 via the downstream plate 30. The desired volumetric flow rate is based on the predetermined amount of fuel within the lean fuel-air mixture that achieves the greatest reduction in NOx emissions for the particular internal combustion engine. The predetermined porosity of the downstream plate 30 will help to assure that only a predetermined amount of fuel-air mixture will mix with the compressed air in the second mixing chamber 32.
It should be understood that the above description is intended for illustrative purposes only, and is not intended to limit the scope of the present invention in any way. Thus, those skilled in the art will appreciate that other aspects, objects, and advantages of the invention can be obtained from a study of the drawings, the disclosure and the appended claims.
